I. Field of the Invention
The present invention relates to a vertical mill that pulverizes a solid matter such as biomass into fine powder.
II. Description of the Related Art
Combustion facilities for boiler power generation and others use fossil fuel, such as coal and heavy oil in many cases. The fossil fuel contributes to global warming due to a CO2 emission problem. Accordingly, the utilization of fuel using biomass as a substitute for the fossil fuel is promoted. The biomass is an organic object resulting from photosynthesis, which includes woody, herbaceous, crops, garbage, and the like. In one of combustion methods using biomass as fuel, a biomass solid matter is pulverized into fine powder and supplied to a pulverized coal-fired boiler. This method is divided into two known methods: a single pulverization method in which coal and biomass are separately pulverized; and a mixture pulverization method in which coal and biomass are mixed and pulverized. In both of the methods, a biomass pulverization device is needed to pulverize a biomass solid matter.
In this case, coal is pulverized by the use of a vertical roller mill, but a biomass solid matter has stretch properties and is inferior in crushability as compared with coal. It is thus difficult to pulverize the biomass solid matter into a predetermined size by the vertical roller mill for coal. Therefore, biomass solid matters are conventionally pulverized by the use of pulverizers such as a hammer mill, a cutter mill, and the like. However, pulverization of a biomass solid matter using a hammer mill, a cutter mill, or the like, requires a great deal of power. This causes deterioration in efficiency of the pulverizers and shortens lifetimes of the pulverizers with the need for maintenance in short-term cycles, which makes it difficult to operate the pulverizers continuously.
The following patent documents and others suggest biomass pulverization devices using a vertical mill. For example, the biomass pulverization device disclosed in Japanese Patent Application Laid-Open No. 2009-291692 presses and pulverizes a biomass solid matter supplied on a rotating pulverization table, by a roller operating in conjunction with rotation of the table, and delivers the pulverized biomass upward by a flowing air current from a lower part, and then classifies the biomass into coarse powder and fine powder. In addition, the biomass pulverization device disclosed in Japanese Patent Application Laid-Open No. 2008-043926 controls a pressing force of a roller and a rotating speed of a table so as to fall within specific ranges in which to facilitate mutual grinding of biomass chips, according to the distance between the roller and the table.